Crosby said the effects are not nearly as bad as what he experienced last January when he sustained hits to the head in successive games. He missed the last half of the 2010-11 season and the first 20 games of this season with a concussion.
"I'm not happy to be watching or to be dealing with this," he said Monday. "I've got a pretty good idea of things now and know this is not where I was before. That's the encouraging part.
"I'm not feeling bad, just have to be careful and make sure I'm 100% before I return."
He missed games against the Philadelphia Flyers and the New York Islanders after taking a number of hits, including the elbow by Krejci and a collision with teammate Chris Kunitz in the game against the Bruins.
"If you had to look at one hit then, yeah ... it was probably that one (by Krejci). It was a good one," Crosby said. "The collision with (Kunitz) was knee-on-knee."
There has been speculation Crosby has some knee issues, but they would take a backseat to the latest brain trauma.
Crosby had a headache after practising last Wednesday and, although he passed an ImPACT baseline test, he said he didn't feel right and the decision was made to hold him out two games.
"You have to listen to your body," he said. "Passing ImPACT was encouraging, but it's not everything. I skated the following day with exertion. I just didn't feel right. After talking with everyone I figured it was better to be cautious and not take any chances. That's where I'm at right now.
"I've been doing light exertion stuff and seeing how that goes. It's that whole (recovery) routine again, but hopefully not as long. When I wasn't doing something for six, seven months that process was a little longer. Hopefully, that's not the case here."
At least Crosby knows what to expect this time around, as much as you can expect anything in dealing with a concussion. "Either you're symptomatic or you're not ... with this kind of stuff, there are so many different things you could call it," he said. "It's not always clear cut. It's not like a (bone) break or anything like that. I'm treating it as I looked at those symptoms before ... it's the same way I'm going to treat them now."
It's disturbing news for anybody who loves hockey, loves watching Crosby compete, for the Penguins, for the NHL.
"I was ready to accept whatever came with playing hockey ... I wasn't expecting it, no," Crosby said.
"I don't know if 'frustrating' even describes it."
This isn't the worst-case scenario, but it's not far off. Crosby took an elbow that hardly anybody else noticed and is out indefinitely again.
You hope for Crosby's sake -- as a person more than the player -- that this won't be a scenario that replays itself: Rest, recovery, return, reinjury.
When Crosby returned Nov. 21 with a spectacular four-point effort against the New York Islanders, it was tempered with the expectation of what would happen when he took a couple of solid hits.
Now, just eight games in, we know and it's not good.
STARS DROPPING LIKE FLIES
It's been a tough few days for the NHL and some of its stars, many of whom find themselves on the shelf with an assortment of upper- and lower-body injuries ... and some in between. Here's a look at some of the big names who are missing in action.
• Sidney Crosby, C, Pittsburgh Penguins. The best player in the game is out indefinitely with a recurrence of concussion-like symptoms. Will miss his third straight game Tuesday.
• Claude Giroux, C, Philadelphia Flyers. Kicked in the head by teammate Wayne Simmonds, he's doubtful for Tuesday's game against the Washington Capitals.
• Chris Pronger, D, Philadelphia Flyers. First diagnosed with a virus, he is now out with a concussion and was to consult with experts in Pittsburgh Monday.
• Jeff Skinner, F, Carolina Hurricanes. One of the most exciting young players in the league, he's doubtful for Tuesday with an upper-body injury after being hit by Edmonton's Andy Sutton.
• Zdeno Chara, D, Boston Bruins. He's expected to be out for three games with a leg injury.
• Mike Green, D, Washington Capitals. He's off to consult a specialist for a lingering groin injury.
• Marty St. Louis, F, Tampa Bay Lightning. Had 499 consecutive games streak snapped when he was hit in the face by a puck in practice. Out indefinitely.
• Mike Richards, C, Los Angeles Kings. Out indefinitely with an upper-body injury.
• Marc Staal, D, New York Rangers. Still out with a concussion.
• Kris Letang, D, Pittsburgh Penguins. Out with a concussion after taking that hit from Montreal's Max Pacioretty.
• Jordan Staal, C, Pittsburgh Penguins. Doubtful for Tuesday's game against Detroit with a lower body injury.
• D Dustin Byfuglien, D, Winnipeg Jets. Doubtful for Tuesday with a leg injury.